Diseases caused by herpesviruses vary from mild to severe, and in some cases, infection with these viruses is life-threatening. Infected cell protein 4 (ICP4) is the major transcriptional regulatory protein of HSV-1. It is intimately involved in the control of viral gene expression during the course of infection. HSV-1 gene expression is regulated in an ordered fashion (Gu, B., et al., Mol. Cell. Biol., 15:3618-3626 (1995); 24, 50), such that three phases of gene expression can be distinguished: the immediate early (IE), early (E), and late (L) genes (Honess, R. W., and Roizman, B., Proc. Natl. Acad. Sci. USA., 72:1276-1280 (1975)). During this process, ICP4 acts as a negative regulator of IE gene expression as a positive transactivator of E and L gene expression (Courtney, R. J., and Benyesh-Melnick, M., Virology, 62:539-551 (1974); (Dixon, R. A. F. and Schaffer, P. A., J. Virol., 36:189-203 (1980); (Kemp, B. E., et al., J. Biol. Chem., 252:4888-4894 (1977); (Preston, C. M., J. Virol., 29:275-284 (1979a); (Preston, C. M., J. Virol., 32:357369 (1979b); Watson, R., and Clements, J. B., Nature (London), 285:329-330 (1980)). Because of its role in activation, ICP4 is absolutely required for viral growth (Godowski, P. J. and Knipe, D. M., Proc. Natl. Acad. Sci. USA, 83:256-260 (1986); (Preston, C. M., J. Virol., 29:275-284 (1979a)).
Genetic analyses of the functional organization of the ICP4 protein have shown the following: residues 143-210 and residues 800-1298 are required for transactivation (Paterson, T., and Everett, R. D., Virology, 166:186-196 (1988); Shepard, A. A., Imbalzano, A. N. and DeLuca, N. A., J. Virol., 63:3714-3728 (1989)); residues 263-487 are required for DNA-binding (Shepard, A. A., Imbalzano, A. N. and DeLuca, N. A., J. Virol., 63:3714-3728 (1989); Wu, C-L. and Wilcox, K. W., J. Virol., 65:1149-1159 (1991)); residues 723-732 are required for nuclear localization (DeLuca, N. A., and Schaffer, P. A., J. Virol., 62:732-743 (1988); Showalter, S. D., Zweig, M. and Hampar, B., Infect. Immun., 34:684-692 (1981)); residues 309-489 including the DNA-binding domain are required for dimerization (Shepard, A. A., Tolentino, P. and DeLuca, N. A., J. Virol., 64:3916-3926 (1990); Wu, C-L. and Wilcox, K. W., Nucl. Acids Res., 18:531-538 (1990)); and residues 171-251 of ICP4 are important for its phosphorylation (DeLuca, N. A., and Schaffer, P. A., J. Virol., 62:732-743 (1988)). Despite the extensive genetic analysis of the ICP4 gene, there is little information available about the phosphorylation on the molecule or its impact on infectivity.
Extensive research has been conducted to identify anti-herpesvirus agents for use in treating infection. For example, acyclovir and vidarabine inhibits viral DNA synthesis. However, vidarabine produces gastrointestinal and neurologic side effects and in some experimental models vidarabine has teratogenic, mutagenic and carcinogenic properties (Fields, B. N., et al., Fields Virology, 2nd ed., 1:448, Raven Press Publ. 1990). In addition, resistance of HSV to acyclovir develops readily in vitro and also occurs in vivo (Fields, B. N., et al., Fields Virology, 2nd ed., 1:450, Raven Press Publ. 1990). New medicaments and assays for identifying them are therefore desirable.